Occasionally proprietary does not mean that it is secret,
but just non-standard, and specific to a particular vendor.
Some proprietary things are still open--with full specifications published. In these cases, they are used
either because the standard didn't do what the
designer wanted, so proprietary may actually be better,
or the proprietary item is selected to lock you into
using their connectors or mounting brackets or whatever.

Sun has a habit of designing
proprietary connectors and then allowing (encouraging) them to become industry standards.

1. In marketroid-speak, superior;
implies a product imbued with exclusive magic by the unmatched
brilliance of the company's own hardware or software designers.
2. In the language of hackers and users, inferior; implies a
product not conforming to open-systems standards, and thus one that
puts the customer at the mercy of a vendor able to gouge freely on
service and upgrade charges after the initial sale has locked the
customer in. Often used in the phrase "proprietary crap".
3. Synonym for closed-source, e.g. software issued in binary
without source and under a restrictive license.

Since the coining of the term open source, many hackers
have made a conscious effort to distinguish between
`proprietary' and `commercial' software. It is possible
for software to be commercial (that is, intended to make a profit
for the producers) without being proprietary. The reverse is
also possible, for example in binary-only freeware.